2012 Annual Report
1a.Objectives (from AD-416):
The long-term objective of this project is to develop sugarbeet (Beta vulgaris L. subsp. vulgaris) breeding lines and populations with resistance to specific diseases and pests. Genes and gene pools from wild beet relatives will be evaluated, characterized, and introgressed into adapted germplasm. Progeny lines and specific breeding materials will be genotyped and phenotyped to determine inheritance patterns and to search for molecular genetic markers. Markers will be validated for usefulness in marker-assisted selection. The efficacy of resistance genes will be evaluated in biological evaluations and replicated trials. The breeding and population improvement program will be continued to accumulate numerous favorable alleles and combine broadly based host plant resistance and high productivity. Over the next 40 months the program will focus on the following objectives:
Objective 1: Analyze the inheritance of disease resistance mechanisms to pathogens common in the United States, especially in the Western growing regions, through mapping sources of disease resistance and identifying phenotypic variation for disease resistance.
Objective 2: Identify novel sources of disease resistance within sugarbeet and its wild relatives to broaden the sugarbeet germplasm base.
Objective 3: Improve sugarbeet germplasm and develop genetic resources through utilization of traditional and molecular breeding tools for release to international sugarbeet seed companies for improved agronomic, quality, disease resistance, and tolerance to abiotic stresses.
1b.Approach (from AD-416):
Develop populations and genetic stocks for mapping qualitative and quantitative sources of disease resistance in sugarbeet. Identify regions of the Beta vulgaris genome associated with phenotypic variation for disease resistance and select advantageous alleles to facilitate marker-assisted selection. Evaluate wild and ancestral relatives of sugarbeet both phenotypically and genotypically for novel sources of disease resistance. Characterize and introgress genetically diverse resistance alleles into enhanced sugarbeet germplasm. Continue a sugarbeet pre-breeding, population, and breeding line improvement program. Integrate genomic tools to develop new germplasm with improved agronomic and quality characteristics and resistance to biotic and abiotic stresses.
Progress was made on all three objectives, which fall under National Program 301, Component 2, Crop Informatics, Genomics, and Genetic Analyses, and Component 3, Genetic Improvement of Crops.
Under Objective 1A, 3 crosses were made to develop genetic stocks and potential mapping populations for sugar beet cyst nematode. 18 potential mapping populations were advanced to the next generation. Of these, 12 were to study the inheritance of rhizomania disease resistance, three for powdery mildew resistance, two for sugar beet cyst nematode (SBCN) resistance. One population was advanced to study inheritance of determinate seed stalk growth.
Under Objective 1B, we screened Beta vulgaris ssp. recombinant inbred lines (RILs). Seed were received from two RIL populations: AYA, developed from the cross C869 (Salinas germplasm) x SP6822 (East Lansing germplasm) and MSR from C869 x Red Beet (W357B). The MSR RILs were developed from the published sugar beet x red beet mapping population. Twenty Five RILs from each population and susceptible and resistant checks were screened under greenhouse conditions for diseases of interest to the Far West growing region including rhizomania, sugar beet cyst nematode, powdery mildew, and Erwinia.
Under Objective 2A, 162 SSR molecular markers were screened on two sets of DNA. The first, product was amplified in four individuals from each of two Bvm accessions (set 1-BVM Individuals) to identify markers polymorphic within or between individuals of each accession. Eleven markers were selected and run on 93 Bvm individuals, two commercial varieties, and one negative control (dH2O) (set 2-BVM 96). Twenty four Bvm accessions from eight countries were represented. Fragment analysis of PCR products was conducted on an Applied Biosystems 3500 genetic analyzer on-site.
Under Objective 3A, continued progress was made on the sugar beet pre-breeding population and line improvement program. At our Salinas locations, we evaluated 3,432 plots comprised of 412 lines, populations, Bvm accessions, and commercial varieties for traits including stand count, reaction to rhizomania, (and powdery mildew and cercospora when naturally present), tons of roots harvested per acre, and percent soluble solids (a measure of percent sucrose). We evaluated 864 plots and 106 lines, populations, Bvm accessions, and commercial varieties in our Brawley field trials for stand count, canopy yellowing due to SBCN, cyst count per plot, and tons of roots harvested per acre.
First ARS-led coded variety trial of commercial varieties under sugar beet cyst nematode field and greenhouse conditions. Sugar beet cyst nematode (SBCN) infestations in the Imperial Valley, California, are a continuing problem that causes sugar and yield losses, and disrupts sugar beet crop rotations. Genetic host resistance is the preferred method of control. For the first time in an ARS-led trial, commercial varieties were evaluated under sugar beet cyst nematode field and greenhouse conditions. Data on stand count, canopy yellowing due to SBCN, tons roots harvested per acre, and cyst count was provided to Beet Sugar Development Foundation member companies and growers to assist with cultivar selection. This is now a yearly trial with new commercial varieties and experimental hybrids added as available and USDA developed germplasm included for comparisons.
Genotypic analysis of samples collected from wild/weedy Beta sp. populations in the Imperial Valley, California. Wild beets were first reported to be present in California’s Imperial Valley in 1928, and have infested sugar beet fields through the present. It is important to understand the origin of these wild Beta sp. populations, identify the species, and determine if there is gene flow between wild and cultivated beets. ARS researchers at Salinas, California, screened 100 wild Beta sp. and 12 weedy sugar beet samples collected from 27 commercial sugarbeet fields in Imperial Valley with 17 SSR molecular markers. Most of the markers amplified only one allele, were designated monomorphic, and not included in further analyses. Seven markers amplified, however, alleles unique to the wild Beta sp. and weedy sugar beet samples, which indicated little or no polymorphism amongst collected wild Beta sp. samples. These results support our hypothesis that there is no gene flow between wild and cultivated beets, a critical observation to the future use of transgenic sugar beets in Imperial Valley.